This proposal represents a concerted effort to determine the chemical and biophysical properties of the peptides in the renin- angiotensin systems and their relation to hypertension. The solution conformation, if any, determined by physical methods and the biologically-active conformation determined by a combination of methods will be correlated. Methods used will include proton C13, F19 NMR and circular dichroism as well as theoretical calculations and restriction of conformational flexibility. Peptides to be studied include angiotensin II, angiotensin I, tetradecapeptide renin substrate, renin inhibitor, bradykinin potentiating factor (which inhibits converting enzyme) and Phe4-Tyr8-angiotensin, a specific competitive inhibitor of angiotensin II. In addition, an attempt will be made to convert the inhibitors from competitive to non-competitive by affinity labels.